In recent years, a lot of progress was made in semi-conductors, electronics, and mechanical technology. The development of high-tech products is starting to head towards minimization and attention to detail. The EDM (electric discharge machining) is one of the main machining methods, and thus many manufacturers are working on improving the discharge power source of the EDM system.
Because of the enhanced emphasis on improving the discharge power source of the EDM system, many manufacturers have begun applying patents for the power source they developed, such as U.S. Pat. No. 6,465,754 B1 from Charmilles Co. Ltd. The circuit of U.S. Pat. No. 6,465,754 B1 uses the AC voltage of ultra hyper frequency in 0.1˜10 MHz to vibrate and collide the positive ions and the negative ions in order to create an arc, without touching the work piece. Therefore, there is no electrolysis on the work piece. After creating the arc, the circuit switches to discharge from the negative electrode to increase the cutting rate of the EDM process. Mitsubishi Co. Ltd. has U.S. Pat. No. 6,727,455 B1 which mentions that the remaining energy in the discharge gap after discharging will affect the discharge gap during the next discharge and the surface roughness of the work piece. So, when alternatively discharging, Mitsubishi Co. Ltd. uses the discharge circuits of opposite polarity to remove the remaining energy in the discharge gap in order to increase the discharging frequency and efficiency. Another company, Sodick Co. Ltd, has published U.S. Pat. No. 6,130,395 A, which uses two DC voltages that correspond to two transistors. First by using rough machining, then precious machining, and then successfully making the surface roughness Rmax smaller than 1 μm. The industrial technology research institute has a patent I 413,559 which uses two set power source modules: a high voltage arcing power module and a low voltage discharging power module. The high voltage arcing power is mainly used for triggering the discharging phenomenon and the low voltage discharging power mainly for machining. After the high voltage arcing, the circuit will detect the voltage to adjust the low voltage and to precisely control each time the machining energy discharges, in order to achieve a high power saving efficiency. Yan Mu-Tian et al. published a patent I 357,840 which is also about the power of an EDM system. The circuit in I 357,840 uses a bridge converter to make a DC power that switches the output power between the positive electrode and the negative electrode in order to stabilize the power supplied and to also prevent electrolysis during the EDM process to decrease the degenerated layer on the work piece. Meanwhile, in the circuit of I 357,840, the circuit for releasing unnecessary voltage during the EDM process is added to prevent a positive (or negative) electrode that is discharging to be affected by a previous negative (or positive) electrode discharging. The circuit for releasing unnecessary voltage during the EDM process can reduce the loss in rapid discharging, increasing the efficiency of the process.
In the current technology for an EDM system there are two kinds of discharging circuits in the EDM system, a transistor discharging circuit, and a single resistance-capacitor discharging circuit. The transistor discharging circuit releases too much power during each discharge, so that removing more material during each discharge makes a quicker machining speed. The problem is that the machining precision is not good enough for micro machining. In view of this, the single resistance-capacitor discharging circuit is often used in micro machining. The single resistance-capacitor discharging circuit uses the charging-discharging principle of a capacitor, in order to generate high currents in a flash, which makes the electron jump between the cutting tool and the work piece and generates a high temperature of almost 10 thousand Celsius to remove the material. Although the high temperature is generated each discharge, each discharge happens in a relatively short time, requires a low amount of energy, and removes small amounts of material. Thus, it can maintain good surface roughness. But the single resistance-capacitor discharging circuit needs to meet the two electrodes in a specific small distance when the capacitor is at full charge and discharging. The known single resistance-capacitor discharging circuit uses a single capacitor for discharging, and thus the discharging times are small in a fixed period of time, causing the machining efficiency to be stagnant.